Copy and paste the below code to your functions.php on your child theme.

add_filter('woofood_rest_line_item_name', 'woofood_hook_replace_title_with_sku', 10, 2);

function woofood_hook_replace_title_with_sku($product_name, $product_id)
{
    global $woocommerce;
    return wc_get_product($product_id)->get_sku();

}

In case you want to use also the product name and SKU you can use the following code

add_filter('woofood_rest_line_item_name', 'woofood_hook_replace_title_with_sku', 10, 2);

function woofood_hook_replace_title_with_sku($product_name, $product_id)
{
    global $woocommerce;
    return $product_name." ".wc_get_product($product_id)->get_sku();

}